Link-shaped structure for a press frame

ABSTRACT

ING USE, THE FILAMENTS OR FIBERS BEING PRESTRESSED AND THE STRESSES THEREIN BEING LOCKED INTO THE MATERIAL, WHEREBY A DESIRED STRESS DISTRIBUTION ACROSS THE CROSS SECTION OF THE MEMBER IS OBTAINED.   A LINK-SHAPED MEMBER HAVING SEMI-CIRCULAR ENDS AND A PAIR OF PARALLEL STRAIGHT SIDE PORTIONS IS MADE OF A FILAMENTARY AND/OR FIBROUS REINFORCED PLASTIC OR RESINOUS MATERIAL, THE FILAMENTS OR FIBERS OF WHICH ARE ORIENTED IN THE DIRECTION OF THE LOOP. THE MEMBER MAY BE A PRESS FRAME WHICH IS ADAPTED TO WITHSTAND TENSILE STRESSER DUR-

Feb. 20, 1973 E. DAVISON LINK-SHAPED STRUCTURE FOR A PRESS FRAME Filed May 27, 1970 2 Sheets-Sheet 1 mHlHm INVENTOR. ERNEST DAVISON ATTORNEYS Feb. 20, 1973 E. DAVISON LINK-SHAPED STRUCTURE FOR A PRESS FRAME 2 Sheets-Sheet 2 Filed May 27 1970 FIG. 5

FIG. 6

INVENIUR. ERNEST DAVISON BY v V ATTORNEYS United States Patent 3,717,024 LINK-SHAPED STRUCTURE FOR A PRESS FRAME Ernest Davison, Cooksville, Ontario, Canada, assignor to Fluid Power Limited, Rexdale, Ontario, Canada Filed May 27, 1970, Ser. No. 40,801 Claims priority, application Great Britain, May 34), 1969,

27,446/69 Int. Cl. B21j 13/04 US. Cl. 72-455 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to the construction of linkshaped members, such as press frames, that are adapted to withstand tensile loads. It is an object of the invention to provide a construction which permits a higher strength to weight ratio than is possible with conventional link constructions.

A press frame usually is of rectangular form, com prising a pair of crossheads which are spaced apart and supported by a pair of upright sidewalls. The main purpose of the frame is to react against the compressive force applied to an object placed between the press platens. Such a rectangular frame is structurally inefficient, because the side walls must provide a bending moment resistance as well as a resistance to the main tensile loads absorbed by the frame sidewalls. The bending moments result from the geometry of the frame structure, and in order to provide the necessary bending moment resistance it is usually necessary to provide crossheads of massive construction.

The problem of bending moments in a press frame can be substantially overcome by making the frame in the form of a chain link, that is to say, in the form of a closed loop having substantially semicircular ends and a pair of parallel straight sidewalls. This construction gives rise to a stress distribution throughout the link which is mainly tensile.

The construction of a chain link is ideally suited to withstand tensile stresses. However, in the case of a heavily loaded chain, such as a ships anchor chain, for example, the maximum tensile stresses may be so high as to necessitate the use of very massive links, causing difficulties of fabrication.

According to the present invention, the above mentioned disadvantages are overcome by providing a press frame in the form of a closed loop having substantially semi-circular ends and a pair of parallel straight side portions, the member being of a filamentary and/or fibrous reinforced plastic or resinous material, the filaments or fibers of which are oriented in the direction of the loop and pre-tensioned so as to hold the material of the loop under compressive stress.

Such a link may be fabricated by providing a former of channel section and the desired shape, and winding the reinforced plastic or resinous material around the former to provide a solid matrix. Instead of winding the matrix onto the former, one may use a nozzle spray moulding technique which suitably orientates the reinforcement material. However, the filament winding process is preferred for the fabrication of press frames, because it permits a controlled winding tension of the reinforcement material, whereby to achieve a reasonably uniform operating stress distribution throughout the cross section of the frame. This condition is obtained by varying the winding tension in a suitable manner across the frame cross section.

Various reinforcement materials for the plastic or resinous matrix include glass and carbon filaments, fine high tensile metal wires, graphite fibers, whisker materials, asbestos and mica fillers.

A link-shaped press frame according to the invention has the following advantages:

(1) high strength to weight ratio;

(2) compactness in relation to load capability; (3) ease of fabrication; and

(4) high fatigue resistance.

It will be appreciated that the former, which is used in the moulding or winding of the matrix, is of no structural significance in the link and can, if the matrix is bonded into a self-supporting rigid mass, be removed.

In order that the invention may readily be understood, various embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of a conventional press;

FIG. 2 is a diagrammatical view, corresponding to FIG. 1, of a press according to the present invention;

FIG. 3 illustrates a press according to the present invention;

FIG. 4 is a section on line 4-4 in FIG. 3;

FIG. 5 illustrates a modified form of press frame according to the invention; and

FIG. 6 is a section on line 66 of FIG. 5.

The press illustrated in FIG. 1 comprises a lower crosshead 1, providing a ram chamber 2, an upper crosshead 3 providing a fixed platen, and a pair of upright sidewalls 4. A movable platen 5 is actuated by a ram 6. It is easily seen that when a compressive force F is applied by the platens, the sidewalls are subjected to a direct tensile stress, indicated by f and also a bending moment reaction B FIG. 2 illustrates a form of press according to the present invention, in which the frame is constructed as a closed loop having substantially semicircular end portions 7, 8, and a pair of parallel, upright side portions 9, 10. A pair of yokes 11 and 12 each of substantially semicircular cross section are arranged in parallel and spaced relation with their flat surfaces opposed to each other, the semicircular end portions 7 and 8 of the frame engaging the curved surfaces of the yokes. The upper yoke 11 provides a fixed platen, and the lower yoke 12 provides a ram chamber 13. When a compressive force P is applied by the movable platen 14, the stresses set up in the frame are mainly tensile, the bending moments at the ends of the upright side portions 9, 10 being substantially eliminated.

A practical embodiment of the press illustrated in FIG. 2 is shown in FIGS. 3 and 4. The press has a link-shaped frame in the form of a closed loop consisting of two substantially semi-circular end portions 15, 16 and two parallel upright side portions 17, 18. The frame consists of a filamentary and/or fibrous reinforced resinous matrix 21 wound upon a channel-sectioned metal former 22. The former 22 also provides attachment points for ancillary equipment. Alternative platen metal guide strips may also be attached to the former. Two semicircular fixed yokes 24, 25 are located in side the ends of the linkshaped frame, the purpose of the yokes being to distribute the applied load as evenly as possible into the frame structure. A movable platen 26, which is actuated by a ram 27, is located and guided by platen guides 23. This ram and its ram chamber may also be fabricated as a filament wound or reinforced matrix component.

In a modification not illustrated, use is made of a reinforced concrete matrix as a surrounding and sup porting structure for the composite ram and ram chamber. The fixed yokes 24, 25 may be of a composite material possessing the desired compressive strength.

The matrix is initially wound onto the former as a web, the reinforcing filaments or fibers extending generally in the direction of length of the web, so that in the final matrix the reinforcing filaments or fibers are oriented in the direction of the closed loop and are pre-tensioned so as to hold the matrix under compressive stress.

A further link structure for a press frame in accordance with the invention is illustrated in FIGS. and 6. This link structure is substantially of the same construction as the link structure shown in FIGS. 4 and 5, but it consists of a number of such frame elements stacked in the manner illustrated in FIG. 6. The elements of the construction shown in FIGS. 5 and 6 are denoted by the same reference numerals as the corresponding elements shown in FIGS. 3 and 4.

The present invention also envisages a link-shaped press frame as described above, but in which the metal former is removed and the elements of the matrix are bonded together by chemical means or by adhesives or cements.

It is also envisaged that provision may be made in some cases to incorporate lubrication within the resinous or plastic matrix, or in a superficial layer adhering to the surface of the matrix. Such lubrication may consist, for example, of molybdenum disulphide or graphite, dispersed in the matrix. Alternatively, adequate lubrication may result from the use of carbon or graphite fibrous filaments and particles embedded in the matrix for reinforcement purposes. The purpose of such lubrication is to provide a proper stress distribution and/or loading alignment within the press, this being achieved by allowin the matrix to slide over the surface of the metal former, and allowing the metal former to slide over the surface of the fixed yokes, or, where the metal former is not incorporated in the press, by allowing the matrix to slide over the surface of the yokes.

A press construction according to the present invention has the property of being self-aligning by reason of the interconnected end yokes of semicircular cross section which are located within the semicircular end portions of the link-shaped frame element.

The advantages of a press frame constructed in accordance with the invention may be summarized as follows:

lightness;

ease of fabrication;

resistance to salt water corrosion;

inherent lubrication properties;

ability to provide an optimum stress distribution throughout the link cross section;

economy of fabrication;

superior strength properties;

a desirable elasticity to avoid shock loading, where a low modulus high strength composite material is employed.

I claim: I 1. A press frame comprising a pair of yokes each of substantially semicircular shape arranged in parallel and spaced relation with their fiat surfaces opposed to each other, spacing means arranged between and engaging the flat surfaces of the yokes, a unitary link-shaped former in the form of a closed loop having substantially semicircular ends with a pair of parallel straight side portions extending between said ends and an outwardly facing open channel extending about its periphery, said former slidably embracing saidyokes and spacing means with its circular ends engaging the curved surfaces of the yokes; and

a solid matrix of plastics material filling said channel and reinforced by filaments which are embedded in the material and oriented in the direction of the loop, the filaments being pretensioned so as to hold the press frame under compressive stress.

References Cited UNITED STATES PATENTS 3,153,898 10/1964 Gerhardt 59-84 3,064,558 11/1962 Von Platen 10()-214 3,450,035 6/1969 Chapman -214 3,503,429 4/1970 Staples 72 45s FOREIGN PATENTS 1,035,615 7/1966 Great Britain 100-214 1,019,533 10/1952 France 100-214 207,730 9/1966 Sweden 100--214 CHARLES W. LANHAM, Primary Examiner G. P. CROSBY, Assistant Examiner U.S. Cl. X.R. 100214 

